Liquid crystal display device

ABSTRACT

A liquid crystal display device includes: a first display panel displaying a first image; a second display panel displaying a second image; and an image processor generating first and second image data based on input video signal. The image processor includes a first differential filtering processor, a multiplier that multiplies a grayscale of the image data subjected to the differential filtering by the first differential filtering processor by a correction coefficient, and a first smoothing processor that performs smoothing processing on image data obtained by adding the image data multiplied by the correction coefficient and the image data based on the input video signal. The image processor generates the first image data based on the image data based on the input video signal and the image data subjected to the smoothing processing, and generates the second image data based on the image data subjected to the smoothing processing.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Japanese application JP2017-068356, filed Mar. 30, 2017. This Japanese application isincorporated herein by reference.

TECHNICAL FIELD

A present invention relates to a liquid crystal display device.

BACKGROUND

A technique, in which two display panels overlap each other and an imageis displayed on each display panel based on an input video signal, isconventionally proposed to improve contrast of a liquid crystal displaydevice (for example, see Unexamined Japanese Patent Publication No.2008-191269). Specifically, for example, a color image is displayed on afront-side (observer-side) display panel in two display panels disposedback and forth, and a black-and-white image is displayed on a rear-side(backlight-side) display panel, thereby improving contrast. In theliquid crystal display device, smoothing processing of spreading locallya portion having a high signal level of the input video signal byseveral pixels is performed on the video signal supplied to therear-side display panel in order to reduce a display defect caused byparallax.

SUMMARY

However, in the conventional liquid crystal display device, because thesmoothing processing is performed by an m pixel-by-m pixel smoothingsize, luminance corresponding to image data output to the rear-sidedisplay panel is lower than luminance corresponding to the input videosignal, and display quality is degraded.

The present disclosure is made in view of the above circumstances, andan object of the present disclosure is to prevent the degradation ofluminance to improve the display quality in a liquid crystal displaydevice in which a plurality of display panels overlap each other.

To solve the above problem, a liquid crystal display device according tothe present disclosure comprises: a first display panel that displays afirst image; a second display panel that displays a second image and isopposed to the first display panel; and an image processor thatgenerates first image data corresponding to the first image and secondimage data corresponding to the second image based on input videosignal. The image processor includes a first differential filteringprocessor that performs differential filtering of detecting a boundaryat which luminance changes in input image data derived from the inputvideo signal, a multiplier that multiplies a grayscale of the image datasubjected to the differential filtering by the first differentialfiltering processor by a correction coefficient settable to a desiredvalue, and a first smoothing processor that performs smoothingprocessing on image data obtained by adding the image data multiplied bythe correction coefficient and the input image data. The image processorgenerates the first image data based on the input image data and theimage data subjected to the smoothing processing, and generates thesecond image data based on the image data subjected to the smoothingprocessing.

In the liquid crystal display device according to the presentdisclosure, the first smoothing processor may perform the smoothingprocessing on the image data based on the input video signal using amean filter having a filter coefficient that becomes a normaldistribution.

In the liquid crystal display device according to the presentdisclosure, the image processor may further include a correctioncoefficient calculator that calculates the correction coefficient suchthat peak luminance of the image data based on the input video signal isequal to peak luminance of the second image data.

In the liquid crystal display device according to the presentdisclosure, a grayscale distribution of the second image data mayinclude a first region in which luminance is substantially equal to peakluminance of the image data based on the input video signal and secondregions on right and left sides of the first region, luminance of thesecond regions being higher than the peak luminance, and a width inwhich the first region and the second regions are added is substantiallyequal to a width of the peak luminance in the grayscale distribution ofthe second image data.

In the liquid crystal display device according to the presentdisclosure, the correction coefficient calculator may include anextension filtering processor that performs extension filtering on theimage data based on the input video signal with a region including atarget pixel and pixels around the target pixel as a filter size, amaximum value of luminance in the filter size being set to luminance ofthe target pixel in the extension filtering.

In the liquid crystal display device according to the presentdisclosure, the correction coefficient calculator may include a seconddifferential filtering processor that performs the differentialfiltering on the image data based on the input video signal, a secondsmoothing processor that performs the smoothing processing on the imagedata subjected to the differential filtering by the second differentialfiltering processor, a third smoothing processor that performs thesmoothing processing on the image data based on the input video signal,an adder that adds a grayscale of the image data subjected to thesmoothing processing by the third smoothing processor and a grayscale ofthe image data subjected to the extension filtering, and a divider thatdivides the grayscale of the image data added, by a grayscale of theimage data subjected to the smoothing processing by the second smoothingprocessor, and the correction coefficient calculator may set acalculation result of the divider to the correction coefficient.

The liquid crystal display device according to the present disclosuremay further comprise: a first grayscale decision unit that decides agrayscale of the first image data according to a gamma characteristic ofthe first display panel based on the input video signal; and a secondgrayscale decision unit that decides a grayscale of the second imagedata according to a gamma characteristic of the second display panelbased on the input video signal, wherein the first differentialfiltering processor may perform the differential filtering on the imagedata in which the grayscale is decided by the second grayscale decisionunit, the correction coefficient calculator may include a seconddifferential filtering processor that performs the differentialfiltering on the image data in which the grayscale is decided by thesecond grayscale decision unit, a second smoothing processor thatperforms the smoothing processing on the image data subjected to thedifferential filtering by the second differential filtering processor, athird smoothing processor that performs the smoothing processing on theimage data in which the grayscale is decided by the second grayscaledecision unit, an extension filtering processor that performs extensionfiltering on the image data in which the grayscale is decided by thesecond grayscale decision unit such that a maximum value of luminance ina filter size is set to luminance of a target pixel with a regionincluding a target pixel and pixels around the target pixel as thefilter size, value of luminance in the filter size being set toluminance of the target pixel, an adder that adds the grayscale of theimage data subjected to the smoothing processing by the third smoothingprocessor and the grayscale of the image data subjected to the extensionfiltering, and a divider that divides the grayscale of the image dataadded, by the grayscale of the image data subjected to the smoothingprocessing by the second smoothing processor. The correction coefficientcalculator may set a calculation result of the divider to the correctioncoefficient, and the first smoothing processor may perform the smoothingprocessing on image data obtained by adding the image data multiplied bythe correction coefficient by the multiplier and the image data in whichthe grayscale is decided by the second grayscale decision unit.

The liquid crystal display device according to the present disclosuremay further comprises: a first grayscale decision unit that decides agrayscale of the first image data according to a gamma characteristic ofthe first display panel based on the input video signal; and a secondgrayscale decision unit that decides a grayscale of the second imagedata according to a gamma characteristic of the second display panelbased on the input video signal, wherein the first differentialfiltering processor may perform the differential filtering on the imagedata in which the grayscale is decided by the second grayscale decisionunit, the correction coefficient calculator may include a seconddifferential filtering processor that performs the differentialfiltering on the image data in which the grayscale is decided by thesecond grayscale decision unit, a second smoothing processor thatperforms the smoothing processing on the image data subjected to thedifferential filtering by the second differential filtering processor, athird smoothing processor that performs the smoothing processing on theimage data in which the grayscale is decided by the second grayscaledecision unit, an extension filtering processor that performs extensionfiltering on the image data based on the input video signal before thegrayscale is decided by the second grayscale decision unit such that amaximum value of luminance in a filter size is set to luminance of atarget pixel with a region including a target pixel and pixels aroundthe target pixel as the filter size, an adder that adds the grayscale ofthe image data subjected to the smoothing processing by the thirdsmoothing processor and the grayscale of the image data subjected to theextension filtering, and a divider that divides the grayscale of theimage data added, by the grayscale of the image data subjected to thesmoothing processing by the second smoothing processor. The correctioncoefficient calculator may set a calculation result of the divider tothe correction coefficient, and the first smoothing processor mayperform the smoothing processing on image data obtained by adding theimage data multiplied by the correction coefficient by the multiplierand the image data in which the grayscale is decided by the secondgrayscale decision unit.

In the liquid crystal display device according to the presentdisclosure, the smoothing processing may be Gaussian filtering.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view illustrating a schematic configuration of a liquidcrystal display device according to the present exemplary embodiment;

FIG. 2 is a plan view illustrating a schematic configuration of afront-side display panel according to the present exemplary embodiment;

FIG. 3 is a plan view illustrating a schematic configuration of arear-side display panel according to the present exemplary embodiment;

FIG. 4 is a sectional view taken along a line A-A′ in FIGS. 2 and 3;

FIG. 5A is a plan view illustrating another example of pixeldispositions of the front-side display panel;

FIG. 5B is a plan view illustrating another example of pixeldispositions of the rear-side display panel;

FIG. 6 is a block diagram illustrating a specific configuration of animage processor according to an exemplary embodiment;

FIG. 7 is a graph representing a relationship between an input gradationand an output gradation;

FIG. 8 is a view illustrating an example of Gaussian filter;

FIG. 9 is a graph illustrating a two-dimensional distribution of afilter coefficient corresponding to a center position of Gaussian filterillustrated in FIG. 8;

FIG. 10 is a block diagram illustrating variation of the imageprocessor;

FIG. 11A illustrates a grayscale of input image A;

FIG. 11B illustrates a grayscale of a second image (output image) withrespect to the input image A;

FIG. 12A illustrates a grayscale of input image B;

FIG. 12B illustrates a grayscale of a second image (output image) withrespect to the input image B;

FIG. 13 illustrates another configuration of an image processor of theexemplary embodiment;

FIG. 14A illustrates a grayscale of input image B;

FIG. 14B illustrates a grayscale of a second image (output image) withrespect to input image B;

FIG. 15 illustrates another configuration of an image processor of theexemplary embodiment;

FIG. 16A illustrates a bright-line image (input image) including abright line;

FIG. 16B is a graph illustrating a distribution of gain factor when thebright-line image in FIG. 16A is input;

FIG. 17A illustrates a bright-line image (input image) including abright line;

FIG. 17B illustrates examples of the bright-line grayscale and abackground grayscale;

FIG. 17C is a graph illustrating a distribution of gain factor when thebright-line image in FIG. 17A is input;

FIG. 18A illustrates a first image;

FIG. 18B illustrates a second image;

FIG. 19A illustrates a combined image in which the first image and thesecond image are combined;

FIG. 19B illustrates a combined image in which the first image and thesecond image are combined;

FIG. 20A illustrates a bright-line grayscale of the bright-line imageand a background grayscale;

FIG. 20B illustrates a distribution of a gain factor;

FIG. 21A illustrates a first image;

FIG. 21B illustrates a second image;

FIG. 22A illustrates a combined image in which the first image and thesecond image are combined; and

FIG. 22B illustrates a combined image in which the first image and thesecond image are combined.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of the present disclosure will bedescribed with reference to the drawings. A liquid crystal displaydevice according to the present exemplary embodiment includes aplurality of display panels that display images, a plurality of drivingcircuits (a plurality of source drivers and a plurality of gate drivers)that drive the display panels, a plurality of timing controllers thatcontrol the driving circuits, an image processor that performs imageprocessing on an input video signal input from an outside and outputsimage data to each of the timing controllers, and a backlight thatirradiates the plurality of display panels with light from a rearsurface side. There is no limitation to a number of display panels, butit is only necessary to provide at least two display panels. When viewedfrom an observer side, the plurality of display panels are disposedwhile overlapping each other in a front-back direction. An image isdisplayed on each of the display panels. Liquid crystal display device10 including two display panels will be described below by way ofexample.

FIG. 1 is a plan view illustrating a schematic configuration of liquidcrystal display device 10 according to the present exemplary embodiment.As illustrated in FIG. 1, liquid crystal display device 10 includesdisplay panel 100 disposed closer to an observer (front side), displaypanel 200 disposed farther away from the observer (rear side) thandisplay panel 100, first timing controller 140 that controls firstsource drivers 120 and first gate drivers 130, first source drivers 120and first gate drivers 130 being provided in display panel 100, secondtiming controller 240 that controls second source drivers 220 and secondgate drivers 230, second source drivers 220 and second gate drivers 230being provided in display panel 200, and image processor 300 thatoutputs image data to first timing controller 140 and second timingcontroller 240. Display panel 100 displays a color image in first imagedisplay region 110 according to the input video signal, and displaypanel 200 displays a monochrome image in second image display region 210according to the input video signal. Image processor 300 receives inputvideo signal Data transmitted from an external system (not illustrated),performs image processing (to be described later) on input video signalData, outputs first image data DAT1 to first timing controller 140, andoutputs second image data DAT2 to second timing controller 240. Imageprocessor 300 also outputs a control signal (not illustrated in FIG. 1)such as a synchronizing signal to first timing controller 140 and secondtiming controller 240. First image data DAT1 is image data fordisplaying the color image, and second image data DAT2 is image data fordisplaying the monochrome image. It is also possible that display panel100 may displays a monochrome image in first image display region 110and display panel 200 may display a monochrome image in second imagedisplay region 210. A backlight (not illustrated in FIG. 1) is disposedon a rear surface side of display panel 200. A specific configuration ofimage processor 300 will be described later.

FIG. 2 is a plan view illustrating a schematic configuration of displaypanel 100, and FIG. 3 is a plan view illustrating a schematicconfiguration of display panel 200. FIG. 4 is a sectional view takenalong a line A-A′ in FIGS. 2 and 3.

A configuration of display panel 100 will be described with reference toFIGS. 2 and 4. As illustrated in FIG. 4, display panel 100 includes thinfilm transistor substrate 101 (hereinafter, TFT substrate) disposed onthe side of backlight 400, opposed substrate 102, which is disposed onthe observer side while being opposite to TFT substrate 101, and liquidcrystal layer 103 disposed between TFT substrate 101 and opposedsubstrate 102. Polarizing plate 104 is disposed on the side of backlight400 of display panel 100, and polarizing plate 105 is disposed on theobserver side.

In TFT substrate 101, as illustrated in FIG. 2, a plurality of datalines 111 (source line) extending in a first direction (for example, acolumn direction), a plurality of gate lines 112 extending in a seconddirection (for example, a row direction) different from the firstdirection are formed, and thin film transistor 113 (hereinafter, TFT) isformed near an intersection between corresponding one of data lines 111and corresponding one of gate lines 112. In planar view of display panel100, a region surrounded by two data lines 111 adjacent to each otherand two gate lines 112 adjacent to each other is defined as one pixel114, and a plurality of pixels 114 are arranged in a matrix form (in therow and column directions). The plurality of data lines 111 are disposedat equal intervals in the row direction, and the plurality of gate lines112 are disposed at equal intervals in the column direction. In TFTsubstrate 101, pixel electrode 115 is formed in each pixel 114, and onecommon electrode (not illustrated) common to the plurality of pixels 114is formed. A drain electrode constituting TFT 113 is electricallyconnected to data line 111, a source electrode constituting TFT 113 iselectrically connected to pixel electrode 115, and a gate electrodeconstituting TFT 113 is electrically connected to gate line 112.

As illustrated in FIG. 4, a plurality of color filters 102 a (coloredportions) each of which corresponds to pixel 114 are formed on opposedsubstrate 102. Each color filter 102 a is surrounded by black matrix 102b blocking light transmission. For example, each color filter 102 a isformed into a rectangular shape. The plurality of color filters 102 ainclude red color filters made of a red (R color) material to transmitred light, green color filters made of a green (G color) material totransmit green light, and blue color filters made of a blue (B color)material to transmit blue light. One of the red color filters, one ofthe green color filters, and one of the blue color filters arerepeatedly arranged in this order in the row direction, color filtershaving the same color are arranged in the column direction, and blackmatrices 102 b are formed in boundaries of color filters 102 a adjacentin the row and column directions. In accordance with color filters 102a, the plurality of pixels 114 include red pixels 114R corresponding tothe red color filters, green pixels 114G corresponding to the greencolor filters, and blue pixels 114B corresponding to the blue colorfilters as illustrated in FIG. 2. In first display panel 100, one pixelgroup 124 is constructed with one red pixel 114R, one green pixel 114G,and one blue pixel 114B, and a plurality of pixel groups 124 arearranged in a matrix form.

First timing controller 140 has a known configuration. For example,based on first image data DAT1 and first control signal CS1 (such as aclock signal, a vertical synchronizing signal, and a horizontalsynchronizing signal), which are output from image processor 300, firsttiming controller 140 generates various timing signals (data start pulseDSP1, data clock DCK1, gate start pulse GSP1, and gate clock GCK1) tocontrol first image data DA1 and drive of first source driver 120 andfirst gate driver 130 (see FIG. 2). First timing controller 140 outputsfirst image data DA1, data start pulse DSP1, and data clock DCK1 tofirst source driver 120, and outputs gate start pulse GSP1 and gateclock GCK1 to first gate driver 130.

First source driver 120 outputs a data signal (data voltage)corresponding to first image data DA1 to data lines 111 based on datastart pulse DSP1 and data clock DCK1. First gate driver 130 outputs agate signal (gate voltage) to gate lines 112 based on gate start pulseGSP1 and gate clock GCK1.

The data voltage is supplied from first source driver 120 to each dataline 111, and the gate voltage is supplied from first gate driver 130 toeach gate line 112. Common voltage V_(com) is supplied from a commondriver (not illustrated) to the common electrode. When the gate voltage(gate-on voltage) is supplied to gate line 112, TFT 113 connected togate line 112 is turned on, and the data voltage is supplied to pixelelectrode 115 through data line 111 connected to said TFT 113. Anelectric field is generated by a difference between the data voltagesupplied to pixel electrode 115 and common voltage V_(com) supplied tothe common electrode. The liquid crystal is driven by the electricfield, and transmittance of backlight 400 is controlled, therebydisplaying an image. In display panel 100, the color image is displayedby supply of a desired data voltage to data line 111 connected to pixelelectrode 115 of each of red pixel 114R, green pixel 114G, and bluepixel 114B. A known configuration can be applied to display panel 100.

Next, a configuration of display panel 200 will be described below withreference to FIGS. 3 and 4. As illustrated in FIG. 4, display panel 200includes TFT substrate 201 disposed on the side of backlight 400,opposed substrate 202, which is disposed on the observer side whilebeing opposite to TFT substrate 201, and liquid crystal layer 203disposed between TFT substrate 201 and opposed substrate 202. Polarizingplate 204 is disposed on the side of backlight 400 of display panel 200,and polarizing plate 205 is disposed on the observer side. Diffusionsheet 301 and/or adhesive sheet are disposed between polarizing plate104 of display panel 100 and polarizing plate 205 of display panel 200.

In TFT substrate 201, as illustrated in FIG. 3, a plurality of datalines 211 (source lines) extending in the column direction, a pluralityof gate lines 212 extending in the row direction are formed, and TFT 213is formed near an intersection between corresponding one of data lines211 and corresponding one of gate lines 212. In planar view of displaypanel 200, a region surrounded by two data lines 211 adjacent to eachother and two gate lines 212 adjacent to each other is defined as onepixel 214, and a plurality of pixels 214 are arranged in a matrix form(the row direction and the column direction). The plurality of datalines 211 are disposed at equal intervals in the row direction, and theplurality of gate lines 212 are disposed at equal intervals in thecolumn direction. In TFT substrate 201, pixel electrode 215 is formed ineach pixel 214, and one common electrode (not illustrated) common to theplurality of pixels 214 is formed. A drain electrode constituting TFT213 is electrically connected to data line 211, a source electrodeconstituting TFT 213 is electrically connected to pixel electrode 215,and a gate electrode constituting TFT 213 is electrically connected togate line 212. Pixel 114 of display panel 100 and pixel of display panel200 are disposed on one-to-one correspondence, and overlap each other inplanar view. For example, red pixel 114R, green pixel 114G and bluepixel 114B, which constitute pixel group 124 in FIG. 2, and three pixels214 in FIG. 3 overlap each other in planar view. It is also possiblethat a relationship between pixel 114 of display panel 100 and pixel 214of display panel 200 is three to one. As illustrated in FIGS. 5A and 5B,one pixel group 124 (see FIG. 5A) composed of red pixel 114R, greenpixel 114G and blue pixel 114B of display panel 100 may overlap onepixel 214 (see FIG. 5B) of display panel 200 in planar view.

As illustrated in FIG. 4, in opposed substrate 202, black matrix 202 bblocking light transmission is formed at a position corresponding to aboundary of each pixel 214. The color filter is not formed in region 202a surrounded by black matrix 202 b. For example, an overcoat film isformed in region 202 a.

Second timing controller 240 has a known configuration. For example,based on second image data DAT2 and second control signal CS2 (such as aclock signal, a vertical synchronizing signal, and a horizontalsynchronizing signal), which are output from image processor 300, secondtiming controller 240 generates various timing signals (data start pulseDSP2, data clock DCK2, gate start pulse GSP2, and gate clock GCK2) tocontrol second image data DA2 and drive of second source driver 220 andsecond gate driver 230 (see FIG. 3). Second timing controller 240outputs second image data DA2, data start pulse DSP2, and data clockDCK2 to second source driver 220, and outputs gate start pulse GSP2 andgate clock GCK2 to second gate driver 230.

Second source driver 220 outputs the data voltage corresponding tosecond image data DA2 to data lines 211 based on data start pulse DSP2and data clock DCK2. Second gate driver 230 outputs the gate voltage togate lines 212 based on gate start pulse GSP2 and gate clock GCK2.

The data voltage is supplied from second source driver 220 to each dataline 211, and the gate voltage is supplied from second gate driver 230to each gate line 212. Common voltage V_(com) is supplied from thecommon driver to the common electrode. When the gate voltage (gate-onvoltage) is supplied to gate line 212, TFT 213 connected to gate line212 is turned on, and the data voltage is supplied to pixel electrode215 through data line 211 connected to said TFT 213. An electric fieldis generated by a difference between the data voltage supplied to pixelelectrode 215 and common voltage V_(com) supplied to the commonelectrode. The liquid crystal is driven by the electric field, andtransmittance of backlight 400 is controlled, thereby displaying animage. The monochrome image is displayed on display panel 200. A knownconfiguration can be applied to display panel 200.

FIG. 6 is a block diagram illustrating a specific configuration of imageprocessor 300. Image processor 300 includes first grayscale decisionunit 311 (first image data generator), first image output unit 312,second image data generator 321, second grayscale decision unit 322,differential filtering processor 323 (first differential filteringprocessor), multiplier 324, adder 325, Gaussian filtering processor 326(first smoothing processor), and second image output unit 327. Imageprocessor 300 performs image processing (to be described later) based oninput video signal Data, and for example, generates first image dataDAT1 of the color image for display panel 100 and second image data DAT2of the black-and-white image for display panel 200. Image processor 300decides a grayscale (first grayscale) of first image data DAT1 and agrayscale (second grayscale) of second image data DAT2 such that acombined gamma value (γ value) of the display image in which the colorimage and the black-and-white image are combined becomes a desired value(for example, γ=2.2).

When receiving input video signal Data transmitted from an externalsystem, image processor 300 transfers input video signal Data to firstgrayscale decision unit 311 and second image data generator 321. Forexample, input video signal Data includes luminance information(grayscale information) and color information. The color information isfor designating the color. For example, in the case that input videosignal Data is constructed with 8 bits, each of a plurality of colorsincluding the R color, the G color, and the B color can be expressed byvalues of 0 to 255. The plurality of colors include at least the Rcolor, the G color, and the B color, and may further include a W (white)color and/or a Y (yellow) color. In the case that the plurality ofcolors include the R color, the G color, and the B color, the colorinformation about input video signal Data is expressed by an “RGB value”([R value, G value, B value]). For example, the RGB value is expressedby [255, 255, 255] in the case that the color corresponding to inputvideo signal Data is white, the RGB value is expressed by [255, 0, 0] inthe case that the color corresponding to input video signal Data is red,and the RGB value is expressed by [0, 0, 0] in the case that the colorcorresponding to input video signal Data is black.

When obtaining input video signal Data, second image data generator 321generates black-and-white image data corresponding to theblack-and-white image using a maximum value (the R value, the G value,or the B value) in each color value (in this case, the RGB value of [Rvalue, G value, B value]) indicating the color information about inputvideo signal Data. Specifically, in the RGB value corresponding totarget pixel 214, second image data generator 321 generates theblack-and-white image data by setting the maximum value in the RGBvalues to the value of target pixel 214. Second image data generator 321outputs the generated black-and-white image data to second grayscaledecision unit 322.

When obtaining the generated black-and-white image data, secondgrayscale decision unit 322 refers to grayscale table (grayscale LUT) todecide the grayscale (second grayscale) corresponding to theblack-and-white image data (second gamma processing). For example,second grayscale decision unit 322 decides the grayscale of theblack-and-white image based on a gamma characteristic for display panel200. For example, as illustrated in FIG. 7, in the gamma characteristicfor display panel 200, an output grayscale changes according to an inputgrayscale in a region where the input grayscale is less than or equal toa predetermined grayscale (64 grayscales), and the output grayscalebecomes 256 grayscales in a region where the input grayscale is higherthan the predetermined grayscale (64 grayscales). Second grayscaledecision unit 322 outputs the black-and-white image data subjected tothe second gamma processing to differential filtering processor 323 andadder 325.

When obtaining the black-and-white image data from second grayscaledecision unit 322, differential filtering processor 323 performsdifferential filtering (also referred to as edge detection processing)on the black-and-white image data to detect (emphasize) a boundary(edge) at which luminance changes largely. For example, differentialfiltering processor 323 performs the differential filtering using aPrewitt filter or a Sobel filter. The differential filtering deletes alow-frequency component, so that the edge at which the luminance changeslargely can be emphasized. A known method can be adopted as thedifferential filtering. Differential filtering processor 323 outputs theblack-and-white image data subjected to the differential filtering tomultiplier 324.

When obtaining the black-and-white image data from differentialfiltering processor 323, multiplier 324 multiplies the grayscale of theblack-and-white image data by gain factor GF (correction coefficient)(multiplication). The grayscale increases by multiplying the grayscaleof the black-and-white image data by gain factor GF. Gain factor GF is avalue calculated by the following equation (4). Control is performedusing gain factor GF such that a linear change can be performed, andgain factor GF is set to a desired value. Multiplier 324 outputs theblack-and-white image data subjected to the multiplication to adder 325.

Adder 325 adds the black-and-white image data obtained from secondgrayscale decision unit 322 and the black-and-white image data obtainedfrom multiplier 324, and outputs an addition result to Gaussianfiltering processor 326.

When obtaining the black-and-white image data from adder 325, Gaussianfiltering processor 326 performs Gaussian filtering on theblack-and-white image data. For example, the Gaussian filtering meansprocessing (smoothing processing) of smoothing an image using a Gaussianfilter (mean filter) having a characteristic of a normal distribution(see the following function expression (1)), in which a weight of afilter coefficient used to calculate a mean value increases as the pixelis closer to the target pixel and the weight of the filter coefficientdecreases as the pixel is farther away from the target pixel.

$\begin{matrix}\left\lbrack {{Mathematical}\mspace{14mu}{Formula}\mspace{14mu} 1} \right\rbrack & \; \\{{f\left( {x,y} \right)} = {\frac{1}{2{\pi\sigma}^{2}}\exp\mspace{11mu}\left( {- \frac{x^{2} + y^{2}}{2\sigma^{2}}} \right)}} & (1)\end{matrix}$

For example, Gaussian filtering processor 326 performs the Gaussianfiltering using a filter having a 27-by-27 pixel region (filter size)illustrated in FIG. 8. FIG. 9 is a graph illustrating a two-dimensionaldistribution (normal distribution) of a filter coefficient correspondingto a center position of the filter (Gaussian filter) illustrated in FIG.8. In the filter of FIG. 8, dispersion coefficient σ of the equation (1)is set to 4.2, and a sum of the filter coefficients corresponding topixels 214 is set to 2¹⁴. For example, Gaussian filtering processor 326decides a calculation result, in which the sum of the values in each ofwhich the grayscale of each of 27 pixels by 27 pixels including thetarget pixel and up and down and right and left 13 pixels (referencepixel) of the target pixel is multiplied by the filter coefficient ofthe filter of FIG. 8 is divided by 214, as the grayscale of the targetpixel in the black-and-white image data obtained from adder 325. Afterperforming the Gaussian filtering on all pixels 214, Gaussian filteringprocessor 326 outputs the black-and-white image data subjected to theGaussian filtering to first grayscale decision unit 311 and second imageoutput unit 327.

Based on input video signal Data received from an external system andthe black-and-white image data obtained from Gaussian filteringprocessor 326, first grayscale decision unit 311 decides the grayscale(first grayscale) of the color image displayed on display panel 100(first gamma processing). For example, first grayscale decision unit 311decides the grayscale of the color image such that the combined image(display image) in which the black-and-white image and the color imageare combined has the combined gamma value of 2.2. First grayscaledecision unit 311 outputs the color image data subjected to the firstgamma processing to first image output unit 312.

First image output unit 312 outputs the color image data (firstgrayscale) to first timing controller 140 as first image data DAT1.Second image output unit 327 outputs the black-and-white image data(second grayscale) to second timing controller 240 as second image dataDAT2. Image processor 300 outputs first control signal CS1 to firsttiming controller 140, and outputs second control signal CS2 to secondtiming controller 240 (see FIGS. 2 and 3).

In the case that an end portion (skirt) of a distribution having a widerange exceeds a filter size in the normal distribution of FIG. 9, in thesecond image, the grayscale of the target pixel becomes higher than anobjective grayscale, and possibly a phenomenon of reversing theblack-and-white (light and darkness) image is generated. The end portionof the normal distribution corresponds to a portion in which the filtercoefficient becomes a minimum value (for example, 0 to 2). The normaldistribution changes according to dispersion coefficient σ of the normaldistribution function (the equation (1)). In the exemplary embodiment,as illustrated in FIG. 9, dispersion coefficient σ is preferably decidedaccording to the filter size such that the end portion of the normaldistribution falls within the filter size. Consequently, the phenomenonof reversing the light and darkness of the second image can beprevented.

Next, a method for calculating gain factor GF illustrated in FIG. 6 willbe described below. Gain factor GF is set such that peak luminance (peakgrayscale) of the input image (in this case, the grayscale decided bysecond grayscale decision unit 322) corresponding to input video signalData is matched with peak luminance (peak grayscale) of the second image(black-and-white image) corresponding to second image data DAT2 (see thefollowing equation (2)).peak luminance of input image=peak luminance of second image  (2)

In the equation (2), the peak luminance of the second image is given bythe following equation (3) corresponding to the configuration in FIG. 6.peak luminance of second image=(peak luminance of inputimage×differential filtering×gain factor GF+peak luminance of inputimage)×Gaussian filtering  (3)

The following equation (4) is obtained when the equation (3) is solvedwith respect to gain factor GF.gain factor GF=(peak luminance of input image−peak luminance of inputimage×Gaussian filtering)/(peak luminance of input image×differentialfiltering×Gaussian filtering)  (4)

FIG. 10 is a block diagram in which gain factor calculator 330(correction coefficient calculator) is added to image processor 300 inFIG. 6. Gain factor calculator 330 expresses a configurationcorresponding to the equation (4). That is, gain factor calculator 330includes differential filtering processor 331 (second differentialfiltering processor), Gaussian filtering processor 332 (second smoothingprocessor), Gaussian filtering processor 333 (third smoothingprocessor), adder 334, and divider 335. Differential filtering processor331 has the same function as differential filtering processor 323, andGaussian filtering processors 332, 333 have the same function asGaussian filtering processor 326.

When obtaining the black-and-white image data from second grayscaledecision unit 322, differential filtering processor 331 performs thedifferential filtering (edge detection processing) on theblack-and-white image data similarly to differential filtering processor323. Differential filtering processor 331 outputs the black-and-whiteimage data subjected to the differential filtering to Gaussian filteringprocessor 332. When obtaining the black-and-white image data fromdifferential filtering processor 331, Gaussian filtering processor 332performs the Gaussian filtering on the black-and-white image data.Gaussian filtering processor 332 outputs the black-and-white image datasubjected to the Gaussian filtering to divider 335.

When obtaining the black-and-white image data from second grayscaledecision unit 322, Gaussian filtering processor 333 performs theGaussian filtering on the black-and-white image data. Gaussian filteringprocessor 333 outputs the black-and-white image data subjected to theGaussian filtering to adder 334.

Adder 334 subtracts the grayscale of the black-and-white image datasubjected to the Gaussian filtering from the grayscale of theblack-and-white image data output from second grayscale decision unit322, and outputs a subtraction result to divider 335.

Divider 335 divides the subtraction result (grayscale) by the grayscaleof the black-and-white image data subjected to the Gaussian filtering bythe Gaussian filtering processor 332. Divider 335 outputs a divisionresult as gain factor GF to multiplier 324.

Examples of the input image and output image in image processor 300having the above configuration will be described. FIG. 11A illustratesan example (input image A) of the input image (the grayscale decided bysecond grayscale decision unit 322). Input image A indicates a minutebright-spot image in which one or a plurality of pixels 214 has 200grayscales (peak luminance) while surrounding (background) pixel 214 has30 grayscales. FIG. 11B illustrates a second image (output image) withrespect to input image A. In image processor 300 of FIG. 10, the peakluminance of the second image is equal to the peak luminance of inputimage A as illustrated in FIG. 11B. Consequently, the objectiveluminance can be obtained in the minute bright-spot image or the minutebright-line image.

In the case that the input image is the bright-spot image (input imageB) in which 20 pixels 214 have 200 grayscales (peak luminance) while thesurrounding (background) pixel 214 has 30 grayscales as illustrated ininput image B of FIG. 12A, width W of a high-luminance region is notspread (or narrowed) although the peak luminance of the second image(output image) is equal to the peak luminance of input image B. Thus, itis difficult to sufficiently reduce the display defect caused by theparallax. In order to solve the problem of the parallax, gain factorcalculator 330 preferably includes extension filtering processor 341 asillustrated in FIG. 13. FIG. 13 illustrates another configuration ofimage processor 300 of the exemplary embodiment. Image processor 300 inFIG. 13 differs from image processor 300 in FIG. 10 in that extensionfiltering processor 341 is added, and the other configuration is thesame.

When obtaining the black-and-white image data from second grayscaledecision unit 322, extension filtering processor 341 performs extensionfiltering on the black-and-white image data. Specifically, extensionfiltering processor 341 performs extension filtering on each pixel 214such that the maximum luminance in a predetermined filter size (forexample, 13 pixels by 13 pixels) is set to the luminance of the targetpixel. The high-luminance region (for example, a white region) extendsas a whole through the extension filtering. The filter size is notlimited to the 13-by-13 pixel region. The filter shape is not limited tothe square shape, but the filter may be formed into a circular shape.

FIG. 14A illustrates input image B identical to that in FIG. 12B. FIG.14B illustrates the second image (output image) corresponding to inputimage B in image processor 300 of FIG. 13. As illustrated in FIG. 14B, agrayscale distribution of the second image includes first region a1 inwhich the luminance is substantially equal to the peak luminance (200grayscales) of input image B, and second regions a2 on right and leftsides of first region a1, the luminance of second regions a2 beinghigher than the peak luminance (200 grayscales). A width in which thefirst region and the second regions are added is substantially equal towidth W1 of the peak luminance of input image B, and the high-luminanceregion of 30 grayscales to 200 grayscales is extended. In imageprocessor 300 of FIG. 13, as illustrated in FIG. 14B, the peak luminanceof the second image is greater than or equal to the peak luminance ofinput image B, and the width of the high-luminance region is widened.Thus, in the wide bright-spot image or bright-line image, the desiredluminance can be obtained, and the problem of the parallax can besolved.

FIG. 15 is a block diagram illustrating a still another configuration ofimage processor 300. The input data input to extension filteringprocessor 341 in image processor 300 in FIG. 15 is different from thatin image processor 300 in FIG. 13, and the other configuration is thesame. In image processor 300 in FIG. 15, the image data prior to thesecond gamma processing performed by second grayscale decision unit 322,namely, the black-and-white image data generated by second image datagenerator 321 is input to extension filtering processor 341. FIG. 16B isa graph illustrating a distribution of gain factor GF in the targetpixel when one pixel 214 (target pixel) inputs the bright-spot image(see FIG. 16A) that becomes the peak luminance. In FIG. 16A, “1”indicates the bright-spot portion and “0” indicates the backgroundportion. As illustrated in FIG. 16B, gain factor GF increases as thegrayscale increases in the bright-spot portion and the grayscaledecreases in the background portion.

FIG. 17A illustrates a bright-line image (input image) including abright line in which one-row pixel 214 becomes the peak luminance, andthe surrounding background of the bright line. FIG. 17B illustratesexamples of a bright-line grayscale (100 grayscales) and a backgroundgrayscale (30 grayscales) of the input image. FIG. 17C is a graphillustrating a distribution of gain factor GF in the target pixel whenthe bright-line image in FIG. 17A is input. When image (the grayscaleprior to the decision of second grayscale decision unit 322) in FIG. 17Bis input, gain factor GF becomes 0.00 by the distribution in FIG. 17C.In image processor 300 of FIG. 15, the second image in FIG. 18B isgenerated when gain factor GF is calculated (GF=0.00). The first imageof FIG. 18A is generated based on the generated second image. For gainfactor GF of 0.00, the second image becomes an image in which thegrayscale is substantially kept constant (flat) because the second imagebecomes an image obtained by performing the Gaussian filtering on theblack-and-white image data decided by second grayscale decision unit 322(see FIG. 18B). In this case, in the first image, deficiency of theluminance in the second image is covered, and the peak luminance becomes135 grayscales (see FIG. 18A). FIG. 19A illustrates the combined image(display image) in which the first image and the second image arecombined. As illustrated in FIG. 19A, the peak luminance of the combinedimage is equal to the peak luminance of the input image (see FIG. 17A)when viewed from a front direction. As illustrated in FIG. 19B, the peakluminance of the combined image is also equal to the peak luminance ofthe input image (see FIG. 17A) when viewed from an oblique direction.Appearance of a flare can be reduced to the minimum as illustrated inFIG. 19B.

FIG. 20A illustrates the input image (the grayscale prior to thedecision of second grayscale decision unit 322) when the bright-linegrayscale of the bright-line image (input image) in FIG. 17A is set to200 while the background grayscale is set to 10. FIG. 20B illustrates adistribution of the same gain factor as FIG. 17C. In the distribution ofFIG. 20B, gain factor GF becomes 0.523 when the image in FIG. 20A isinput. In image processor 300 of FIG. 15, the second image in FIG. 21Bis generated when gain factor GF is calculated (GF=0.523). A first imageof FIG. 21A is generated based on the generated second image. In thefirst image, the deficiency of the luminance in the second image isallocated, and the peak luminance becomes 255 grayscales. This meansthat gain factor GF is calculated such that the maximum value in whichthe luminance can be corrected is selected in the first image. FIGS. 22Aand 22B illustrate the combined image (display image) in which the firstimage and the second image are combined. As illustrated in FIG. 22B, thepeak luminance of the combined image is lower than the peak luminance ofinput image (see FIG. 20B) when viewed from the oblique direction. Asillustrated in FIG. 22A, the peak luminance of the combined image isequal to the peak luminance of input image (see FIG. 20B) when viewedfrom the front direction. For the bright-line image in FIG. 20A, theluminance is corrected until the first image reaches a breaking point of255 grayscales. However, the uncorrectable luminance exceeding 255grayscales is assured in the second image. Thus, the flare remainsslightly as illustrated in FIG. 22B. However, the flare can be reducedto an extent in which the display quality is not degraded.

At this point, the grayscale of the combined image (display image) isexpressed by (grayscale of first image)×(grayscale of second image)/255grayscales. For this reason, when the grayscale of the second image isexcessively lowered, the grayscale of the first image increasesexcessively, and the adjustment can hardly be performed. When thegrayscale of the second image changes steeply, the flare of the combinedimage is easily visually recognized. On the other hand, in theconfiguration of the exemplary embodiment, image processor 300 keeps thegrayscale of the second image substantially constant (flat), andproperly shares the grayscale of the first image and the grayscale ofthe second image such that the deficiency of the luminance in the secondimage is covered by the first image. Consequently, the appearance of theflare can be reduced to the minimum while the luminance of the brightspot is assured.

Liquid crystal display device 10 of the present disclosure is notlimited to the above configuration. For example, in the configuration,the Gaussian filtering with the normal distribution function (seeequation (1)) is described as an example of the smoothing processingperformed by the first smoothing processor. However, the smoothingprocessing is not limited the above example. The smoothing processingmay be processing with a window function such as a Hanning window, aflat-top window, a Blackman-Harris window, and a Kaiser-Bessel window orprocessing with a simply conical filter.

In the above, the specific embodiments of the present application havebeen described, but the present application is not limited to theabove-mentioned embodiments, and various modifications may be made asappropriate without departing from the spirit of the presentapplication.

What is claimed is:
 1. A liquid crystal display device comprising: afirst display panel that displays a first image; a second display panelthat displays a second image and is opposed to the first display panel;and an image processor that generates first image data corresponding tothe first image and second image data corresponding to the second imagebased on input video signal, wherein the image processor includes afirst differential filtering processor that performs differentialfiltering of detecting a boundary at which luminance changes in inputimage data derived from the input video signal, a multiplier thatmultiplies a grayscale of the image data subjected to the differentialfiltering by the first differential filtering processor by a correctioncoefficient settable to a desired value, and a first smoothing processorthat performs smoothing processing on image data obtained by adding theimage data multiplied by the correction coefficient and the input imagedata, and the image processor generates the first image data based onthe input image data and the image data subjected to the smoothingprocessing, and generates the second image data based on the image datasubjected to the smoothing processing, wherein the image processorfurther includes a correction coefficient calculator that calculates thecorrection coefficient such that peak luminance of the input image datadetermines peak luminance of the second image data.
 2. The liquidcrystal display device according to claim 1, wherein the first smoothingprocessor performs the smoothing processing on the input image datausing a mean filter having a filter coefficient that becomes a normaldistribution.
 3. The liquid crystal display device according to claim 1,wherein a grayscale distribution of the second image data includes afirst region in which luminance is substantially equal to peak luminanceof the input image data and second regions on right and left sides ofthe first region, luminance of the second regions being higher than thepeak luminance, and a width in which the first region and the secondregions are added is substantially equal to a width of the peakluminance in the grayscale distribution of the second image data.
 4. Theliquid crystal display device according to claim 1, wherein thecorrection coefficient calculator includes an extension filteringprocessor that performs extension filtering on the input image data witha region including a target pixel and pixels around the target pixel asa filter size, a maximum value of luminance in the filter size being setto luminance of the target pixel in the extension filtering.
 5. Theliquid crystal display device according to claim 1, wherein thecorrection coefficient calculator includes a second differentialfiltering processor that performs the differential filtering on theinput image data, a second smoothing processor that performs thesmoothing processing on the image data subjected to the differentialfiltering by the second differential filtering processor, a thirdsmoothing processor that performs the smoothing processing on the inputimage data, an adder that adds a grayscale of the image data subjectedto the smoothing processing by the third smoothing processor and agrayscale of the image data subjected to the extension filtering, and adivider that divides the grayscale of the image data added by the adder,by a grayscale of the image data subjected to the smoothing processingby the second smoothing processor, and the correction coefficientcalculator sets a calculation result of the divider to the correctioncoefficient.
 6. The liquid crystal display device according to claim 1,further comprising: a first grayscale decision unit that decides agrayscale of the first image data according to a gamma characteristic ofthe first display panel based on the input video signal; and a secondgrayscale decision unit that decides a grayscale of the second imagedata according to a gamma characteristic of the second display panelbased on the input video signal, wherein the first differentialfiltering processor performs the differential filtering on the imagedata in which the grayscale is decided by the second grayscale decisionunit, the correction coefficient calculator includes a seconddifferential filtering processor that performs the differentialfiltering on the image data in which the grayscale is decided by thesecond grayscale decision unit, a second smoothing processor thatperforms the smoothing processing on the image data subjected to thedifferential filtering by the second differential filtering processor, athird smoothing processor that performs the smoothing processing on theimage data in which the grayscale is decided by the second grayscaledecision unit, an extension filtering processor that performs extensionfiltering on the image data in which the grayscale is decided by thesecond grayscale decision unit such that a maximum value of luminance ina filter size is set to luminance of a target pixel with a regionincluding a target pixel and pixels around the target pixel as thefilter size, an adder that adds the grayscale of the image datasubjected to the smoothing processing by the third smoothing processorand the grayscale of the image data subjected to the extensionfiltering, and a divider that divides the grayscale of the image dataadded by the adder, by the grayscale of the image data subjected to thesmoothing processing by the second smoothing processor, the correctioncoefficient calculator sets a calculation result of the divider to thecorrection coefficient, and the first smoothing processor performs thesmoothing processing on image data obtained by adding the image datamultiplied by the correction coefficient by the multiplier and the imagedata in which the grayscale is decided by the second grayscale decisionunit.
 7. The liquid crystal display device according to claim 1, furthercomprising: a first grayscale decision unit that decides a grayscale ofthe first image data according to a gamma characteristic of the firstdisplay panel based on the input video signal; and a second grayscaledecision unit that decides a grayscale of the second image dataaccording to a gamma characteristic of the second display panel based onthe input video signal, wherein the first differential filteringprocessor performs the differential filtering on the image data in whichthe grayscale is decided by the second grayscale decision unit, thecorrection coefficient calculator includes a second differentialfiltering processor that performs the differential filtering on theimage data in which the grayscale is decided by the second grayscaledecision unit, a second smoothing processor that performs the smoothingprocessing on the image data subjected to the differential filtering bythe second differential filtering processor, a third smoothing processorthat performs the smoothing processing on the image data in which thegrayscale is decided by the second grayscale decision unit, an extensionfiltering processor that performs extension filtering on the image databased on the input video signal before the grayscale is decided by thesecond grayscale decision unit such that a maximum value of luminance ina filter size is set to luminance of a target pixel with a regionincluding a target pixel and pixels around the target pixel as thefilter size, an adder that adds the grayscale of the image datasubjected to the smoothing processing by the third smoothing processorand the grayscale of the image data subjected to the extensionfiltering, and a divider that divides the grayscale of the image dataadded by the adder, by the grayscale of the image data subjected to thesmoothing processing by the second smoothing processor, the correctioncoefficient calculator sets a calculation result of the divider to thecorrection coefficient, and the first smoothing processor performs thesmoothing processing on image data obtained by adding the image datamultiplied by the correction coefficient by the multiplier and the imagedata in which the grayscale is decided by the second grayscale decisionunit.
 8. The liquid crystal display device according to claim 1, whereinthe smoothing processing is Gaussian filtering.